The present invention relates to highly sensitive strain gages having a thin discontinuous metal layer which changes its resistance with strain and has improved stability.
Strain gages as transducers for strain gages based on the physical effect of an electrical conductor changing its resistance under mechanical load, eg. strain, have long been known and are used, for example, for measuring strains in components as a result of static or dynamic loads. In conventional wire or foil strain gages, in general wire wound into a coil is embedded in plastic and is connected firmly to the object being investigated. Because of the linear coupling of strain and change in resistance, strains .epsilon. of less than 10.sup.-6 cannot be resolved. The relevant prior art includes, for example, U.S. Pat. Nos. 2,556,132 and 2,621,276 and the monograph Strain Gauge Technology by A.L. Window and G.S. Holister, Applied Science Publishers Ltd., Essex, England, 1982, particularly pages 1 to 39. Semiconductor strain gages have a higher sensitivity but have the disadvantage of greater temperature dependence.
However, in many fields, such as research into creep processes, inelastic deformation, phase transitions, geological deformation processes in rock or ice, etc., the measurement of strains .epsilon. of less than 10.sup.-6 is important.
Investigations into discontinuous metal layers on dielectrics, such as layers of gold, silver, palladium or tin on glass or quartz substrates, are known (cf. Advances in Physics 24 (1975), 407-461 and J. Appl. Phys. 34 (1963), 2700-2708. The disadvantage of the systems investigated is their structural instability due to diffusion-controlled aging processes in the discontinuous metal layers, which leads to a shift in the distribution of distances between the metallic islands of the layer toward larger distances. This results in a rapid increase in the electrical resistance of the discontinuous metal layers investigated, and finally to suppression of the tunnel currents in the discontinuous metal layer and to electrical insulation.